1. Technical Field
The present disclosure relates to a control device of a plurality of switching converters.
2. Description of the Related Art
In the prior art, multiple converters are known; they are made by means of a parallel combination of two or more switching converters in any of the standard types (for example, buck, flyback, boost, etc.), typically the same for all, in such a way that they share the same voltage source and dispense power on the same load. If then in such converters control methods are actuated, that fundamentally consist of staggering in an appropriate manner the PWM pulse trains that control each converter, it is more proper to speak of “multiphase” converters.
Multiple and multiphase approaches are used when with a single converter it is impossible or economically disadvantageous to comply with design specifications. The most common situation in which such approaches may be suitable is at a high level of power current. In fact, total power or current could equally be subdivided by a number n of converters, each one of which would be scaled to carry an N-th thereof. In addition to this, in the specific context of the multiphase approach, with an appropriate time control of the PWM pulse trains of the single converters it is possible to bestow on the totality thereof properties that are not detectable individually. For example, it is possible to minimize or even, in certain cases, to zero the ripple current at the input (or at the output) of the totality of converters, thereby optimizing stress and thus minimizing the bench cost of capacitors affected by optimization; or, still with a suitable control method, the overall system can be made equivalent to one that works at a frequency that is the same as the sum of the individual frequencies, thereby enabling the dimensions of the magnetic parts to be minimized and dynamic performances to be obtained that are inconceivable with a single converter.
FIG. 1 shows a two-phase buck converter used to supply the modern processors present in desktop and notebook PCs. This approach is characterized by very low supply voltages (less than 1.8V), by high consumption (greater than 90 A), and by very high consumption dynamics (greater than 1 A/ns). Below, specific reference will be made to multiphase converters; nevertheless, it is noted that all the remarks that will be made remain valid also in the simpler case of a multiple approach.
As already mentioned, a primary requirement that leads to the use of multiphase converters is the high power level. In this case, the maximum benefit from the use of a multiplicity of converters is derived when the system is called upon to work at full load, whereas with reduced loads to have many converters available leads to redundancy. Except for some cases in which redundancy is required in the supply system to ensure very high levels of service continuity, in general this constitutes a waste. Furthermore, at reduced loads, the loss of energy associated with the control (for example the driving of FET transistors), and a series of losses of energy regardless of the load (for example losses associated with loading and unloading stray capacitance of the power elements) begin to become significant and the conversion efficiency of the system (i.e., the ratio between the power returned to the load and the power absorbed by the input source) starts to deteriorate rapidly.
In many systems, which may have non-operational so-called standby conditions, in which there is an extremely reduced load for the converter that supplies them, conformity to voluntary standards or recommendations is requested that aim to regulate the reduction of the energy consumption of such appliances in the aforementioned conditions (e.g., EnergyStar, Energy2000, Blue Angel, etc.). In this case, the reduction of energy losses mentioned above becomes essential for achieving conformity.
If, sometimes, it is not an easy task to ensure that the consumption of a single converter falls within the recommended limits. It can be easily imagined how this task is further aggravated by the presence of several converters. There is thus the need to adapt known techniques for single converters to multiple or multiphase converters or to complement them with new ones specific to such converters in such a way as to facilitate the task of the system designer.
Various techniques are known for minimizing low or zero load consumption for single converters and all involve, substantially, the reduction of the operating frequency of the converter in the above conditions. In a multiphase converter composed of N single converters (namely an N-phase converter), any one of such techniques can be applied to each of the N converters of the totality. Thus if Pin0 is the input power absorbed by the single converter (for the sake of simplicity considered the same for all) in load conditions, for example zero, the power absorption in such conditions for the N-phase converter will be N·Pin0. Although Pin0 is small, N·Pin0 could exceed the limits envisaged for the power class to which the N-phase converter belongs if N is large enough.